1. Field of the Invention
The present invention relates to a recording of contents information recorded with an electronic watermark signal therein, particularly, relates to a recording apparatus and a recording method of an electronic watermark, wherein an electronic watermark signal is always held when a part of contents information is extracted and recorded.
2. Description of the Related Art
An electronic watermark is a technique of embedding a certain information in a multimedia data such as image and sound and concealing the certain information. Various methods of concealing are provided.
The NTT Human Interface Laboratory reported “An Embedding Method of Copyright Information using DCT for Digital Moving Pictures” in the SCIS'97-31G. It proposes the method of embedding information in the MPEG (Moving Picture Experts Group) code, particularly, the method of embedding information based upon alteration of DCT (discrete cosine transform) coefficient, a motion vector and quantization characteristics.
The Defense Academy of Japan reported “A Method of Signing Watermark on a Picture by PN Succession” in the SCIS'97-26B. It proposes the method of diffusing a picture signal by the PN succession and synthesizing a signature information with the picture in accordance with the direct diffusion method.
G. Caronni proposed that a tag, which is a small geometrical pattern, be added to an electronically processed picture in an intensity level, which is hardly perceived visibly, is proposed in the thesis titled “Assuring Ownership Rights for Digital Images” in the Proc. Reliable IT Systems, VIS '95, 1995. A method of embedding an electronic watermark signal, which resembles to quantization noise is described in the theses “Embedding Secret Information into a Dithered Multi-level Image” in the IEEE Military Comm. Conference, pp. 216-220, 1990 by K. Tanaka and “Video-steganography” in the IMA Intellectual Property Proc., VI, pp. 187-206, 1994 by K. Mitsui et al. respectively.
A method of inserting an electronic watermark signal into a pixel allocated in a vicinity of an outline of a picture in the least significant bit is described in the thesis titled “Cryptology for Digital TV Broadcasting”, Proc. Of the IEEE, 83(6), pp. 944-957, 1995, by Macq and Quisquater.
A statistical method called “patchwork” and a method of utilizing a random texture pattern, which is shown in a picture called “texture block coding” is explained in the thesis titled “Techniques for Data Hiding”, Proc. of SPIE, v2420, page 40, July 1995, by W. Bender et al.
MPEG signal, which is one of compressed signals, to be inserted with an electronic watermark signal is depicted next. Essentially MPEG is a name of an organization, “Moving Picture Experts Group”. However, it currently represents standards or specifications for coding signals. Accordingly, MPEG is composed of several techniques
FIG. 6 shows a block diagram of the MPEG encoder according to the prior art.
In FIG. 6, the MPEG encoder comprises a predictor 41 for motion compensation, a subtracter 42, a discrete cosine transformer (DCT) 43, a quantizer 44, a VLC (variable length coder) 45, a buffer 46, an inverse-quantizer 47, an inverse-DCT 48, an adder 49 and a memory 50 for picture.
In the subtracter 42, a difference between an input picture signal and a locally decoded picture, which is predicted for motion compensation by the predictor 41, is subtracted from the input pickup signal. Accordingly, a time redundancy portion is deleted from the input picture signal. There exist 3 modes of predicting directions “past”, “future” and “both past and future”. Further, these modes can be used by switching each macro block (MB) of 16 pixels multiplied by 16 pixels. A direction of prediction is decided by a picture-type given to the input picture signal. There exists 2 modes of “predicting from past” and “encoding an MB independently without predicting” in a predictive coded picture (P-picture). There exists 4 modes of predicting future”, “past”, “both past and future” and “encoding a MB independently without predicting” in a bi-directionally predictive coded picture (B-picture). Furthermore, encoding all MBs independently is an intra-coded picture (I-picture).
A motion vector is detected with the accuracy of half pel or half-pixel after performing a pattern matching of a motion area at each MB and motion compensation is predicted by shifting it with a motion component. There exists 2 directions of horizontal and vertical in a motion vector. The direction is transmitted as an additional information of MB in conjunction with a motion compensation (MC) mode, which indicates a prediction. From a first I-picture to a picture preceding a second I-picture is called a group of pictures (GOP). In a case that the GOP is used in storage media such as an optical recording medium and a magnetic recording medium, approximately 15 pictures are used in general.
A differential picture is orthogonally transformed in the DCT 43. According to MPEG, the 2-dimentional DCT is applied to a DCT block of 8×8 with dividing one MB into 4. Generally, a video ail signal contains more low frequency components and less high frequency components, so that DCT coefficients converge into low frequency components if the DCT is applied.
The picture data (DCT coefficient) applied by the DCT is quantized by the quantizer 44.
The quantized data is processed with the variable length coding (VLC) by the VLC 45.
The data coded by VLC is temporarily stored in the buffer 46 and outputted as a coded data in a predetermined transfer rate. A generated coding amount per MB of the data to be outputted is transferred to a code amount limiter not shown. The code amount limiter controls a quantizing scale by feeding an error code amount, which is a difference between the generated code amount and a target code amount, back to the quantizer 44 for controlling the generated code amount.
Further, the quantized picture data is inversely quantized by the inverse-quantizer 47 and inversely discrete cosine transformed by the inverse-DCT 48, and temporarily stored in the memory 50 through the adder 49, and then the quantized picture data is used in the predictor 41 for motion compensation as reference of a decoding picture or a local decoding picture so as to calculate a differential picture.
The coded data outputted from the buffer 46 is decoded through an inverse process of coding.
FIG. 7 shows a block diagram of the MPEG decoder according to the prior art.
In FIG. 7, the MPEG decoder comprises a variable length decoder (VLD) 51, an inverse-quantizer 52, an inverse-DCT 53, an adder 54, a memory 55 for a picture and a predictor 56 for motion compensation.
With respect to an insertion frequency of electronic watermark signals in the prior art mentioned above, it depends upon the application. For example, in the case of picture data, electronic watermark signals are scattered by using several frames of pictures. In this case, it shall be a configuration of combining several frames. Otherwise there exists a problem that an electronic watermark signal cannot be read out. Further, a case that an electronic watermark signal is recorded in one frame at each of several frames can be considered. In this case, there exists another problem that an electronic watermark signal may disappear from a frame recorded with an electronic watermark signal if a frame not recorded with an electronic watermark signal is extracted.
An electronic watermark signal is not always recorded in a data, which is extracted from a specific area in a frame, even though an electronic watermark signal is recorded in each frame.
Furthermore, in a case of audio data, there exists a case that electronic watermark signals are scattered in the audio data using a specific number of samples. In this case, it shall be a configuration of combining the specific number of samples. Otherwise an electronic watermark signal cannot be read out.